Conventional warming apparatuses for canned beverages used in grocery stores are adapted to heat canned beverages in a glass case and to keep the canned beverages at a preset temperature. Therefore, consumers are allowed to purchase the warmed beverages in the glass case. Thus, the warming apparatus of this kind is adapted to keep the canned beverages at the desired temperature by raising a temperature in the glass case to the desired temperature. For this purpose, it is necessary to always energize a heating device of the warming apparatus. This means that the conventional warming apparatuses of this kind consume electricity continuously and a running cost thereof is therefore expansive. In addition, oxidation reactions of ingredients (e.g., vitamin C, starch, etc.) of the beverage are promoted by thus keeping the beverage warm, and as a result, color, flavor, taste etc. of the beverage in the can will be deteriorated. Thus, it is not preferable to keep the canned beverages in the warming apparatus. In order to avoid such disadvantages, heating apparatuses for heating the canned beverages quickly according to need have been proposed.
For example, Japanese Patent No. 3259808 discloses a heating device for canned drink adapted to heat a canned drink by applying high-frequency current to a heating coil wound around the can held by a rotary table rotated by a motor. Specifically, the can is held by a cylindrical guide except for an upper portion, and a temperature of the can is detected by a thermistor bolometer, a thermopile or the like at the exposed upper potion. Therefore, a heating of the can is stopped when the temperature of the upper portion of the can is raised to a preset temperature.
Japanese Patent No. 4562765 discloses an induction heating apparatus for a resealable metal beverage can sealed by a cap screwed onto a threaded neck portion (as will be called a resealable can hereinafter). The induction heating apparatus taught by Japanese Patent No. 4562765 is comprised of a heating coil wound around a cylindrical holder, and adapted to heat the resealable can held in the holder by energizing the coil to generate an induced current while rotating the holder. According to the teachings of Japanese Patent No. 4562765, in order to enhance an agitation effect, the holder is inclined with respect to a vertical line and the holder is rotated while changing a revolution speed.
Japanese Patent Laid-Open No. 2000-11247 discloses another induction heating device for canned beverage in which the can is placed sideways on a heating coil. According to the teachings of Japanese Patent Laid-Open No. 2000-11247, the induction heating device is comprised of rollers contacted with an outer surface of a can trunk, and those rollers are individually provided with a spiral groove or ridge. Therefore, the can is moved in an axial direction by rotating the rollers by a motor. In order to enhance an agitation effect, a rotational direction of the can is reversed repeatedly.
Thus, according to the teachings of Japanese Patent No. 3259808, the can is heated by applying high-frequency current to the heating coil wound around the can while rotating the can so that the content is heated by the heat of the can. However, if the can contains high viscosity beverage such as a corn soup, it is difficult to create a convection flow of the beverage by the heat of the can. In this case, therefore, the contents may be heated only in the vicinity of the inner face of the can and the central portion of the contents may not be heated sufficiently. In addition, as a result of heating the beverage can by the induction heating, the can itself produces a heat so that the surface temperature of the can is raised to be higher than that of the of the content. Therefore, if the heating is stopped at an instant when the temperature measured at the surface of the can reaches a preset temperature, the temperature of the content may be lower than the preset temperature.
Meanwhile, according to the teachings of Japanese Patent No. 4562765, the resealable can is heated by energizing the coil wound around the cylindrical holder. In this case, if the temperature of the can trunk is measured in the vicinity of the heating portion, the temperature of the can thus measured may be different from an actual temperature of the content.